In wireless communications systems, such as cellular networks, bandwidth is often a valuable resource that should be conserved. Thus, there is a need for compression techniques. Currently, there are known compression techniques that are suitable for the compression of arbitrary data units, such as protocol packet payloads. These techniques involve compression algorithms, which vary from being mathematical (e.g., gzip) to grammatical (e.g., SDP dictionaries translating text fields to a bit encoded format).
In the case of Internet Protocol (IP) based communications, overhead associated with packet headers consumes a considerable amount of communications bandwidth. For instance, an Internet Protocol, version 4 (IPv4) packet header requires 20 bytes, while an Internet Protocol, version 6 (IPv6) packet header requires 40 bytes. To address the amount of bandwidth consumed by packet headers, specialized compression schemes have been developed that are more effective on packet headers than general-purpose compression algorithms. In particular, specialized schemes have been developed for UDP/IP, ESP/IP and RTP/UDP/IP packets. For instance, one known header compression scheme is Robust Header Compression (ROHC). Another known header compression scheme is disclosed in M. Degermark et al., “IP Header Compression,” RFC 2507, The Internet Society, February 1999 (“RFC 2507”). This document is incorporated herein by reference in its entirety and may be downloaded from http://www.ietf.org/rfc/rfc2507.txt.
However, existing work on packet header compression has focused on audio/video streaming services such as Voice over IP employing RTP/UDP/IP transport. To this end, header compression is a known technique, especially for IP streaming where RTP/UDP/IP headers may be compressed from around 60 bytes to below 5 bytes.
The Reliable Multicast Transport (RMT) Working Group of the Internet Engineering Task Force (IETF) is in the process of standardizing two categories of error-resilient multicast transport protocols. In the first category, reliability is provided through the use of forward error correction (FEC). In the second category, reliability is provided through the use of receiver feedback. Asynchronous Layered Coding (ALC) is a protocol instantiation belonging to the first category, while the NACK-Oriented Reliable Multicast (NORM) protocol belongs to the second category. These protocols employ UDP and IP protocols and may be used in various types of wireless multiple-access networks such as UMTS, WLAN, DVB-T and DVB-S.
The ALC and NORM protocols are designed for the delivery of discrete binary objects, such as downloadable files. When deployed on wireless networks, it is desirable for these protocols to conserve bandwidth. Packet payload compression schemes such as gzip can be readily used for RMT protocols. However, the current options for compressing the headers of these protocol packets are limited. At best, ROHC only compresses UDP/IP portions of these packets. Also, the IP header compression scheme of RFC 2507 only compresses the headers of the IP protocol. In addition, this protocol has problems with transmission errors. Another compression mechanism, known as DEFLATE also causes problems with transmission errors because it does not provide any support for error recovery.